1. Field of the Invention
The present invention relates to a padless high density circuit board and a manufacturing method thereof, and more specifically to a padless high density circuit board for assembling an electronic product and a manufacturing method thereof.
2. Description of the Related Art
Due to the demand for small-aspect, light and powerful electronic products, it is necessary for a design rule of a circuit board includes, for example, a substrate for a flip chip, BGA, or other kinds of assembly or a printed circuit board (PCB) to assemble an IC package, a light-emitting device, a connector, a passive device, another one circuit board, or other kinds of device, to lay out denser wiring in a limited area of the circuit board. The design rule for external wiring terminal is a major factor limiting wiring density of the circuit board.
In FIG. 1, a conventional substrate 100 for flip chip assembly, for example, shows how the design rule for the external wiring terminal limits wiring density of the circuit board. Bonding pad 112 is an external terminal of external wiring 110. R1, the diameter of bonding pad 112, is as about two to ten times W, the line width of trace line 114 of external wiring 110. Line pitch of external wiring 110, a distance between two neighboring trace lines 114, is limited by the diameter of bonding pad 112. To stay free of short circuits in external wiring 110, it is necessary that the distance between two neighboring trace lines 114 be larger than half (W+R1), not negatively affecting the design of wiring for a circuit board with a line pitch larger than 180 μm, but that of wiring for a circuit board, such as external wiring 110 of substrate 100 for flip chip assembly, with a line pitch as large as 180 μm, resulting from a bump pitch of an IC chip (not shown) predetermined to attach to substrate 100 being usually as large as 180 μm or below. The design of external wiring 110 is usually limited by the diameter of bonding pad 112, resulting in increased wiring layers or area of substrate 100 to involve all the necessary wiring, resulting from the negative to shrink the distance between two neighboring trace lines 114. Thickness, area, and manufacturing cost of substrate 100 are therefore increased, and the aspect and weight of a final product using substrate 100 are also negatively affected. The design of wiring for other kinds of circuit board includes, for example, a substrate for BGA or other kinds of assembly, or a PCB to assemble an IC package, a light-emitting device, a connector, a passive device, another one circuit board, or other kinds of device, faces the same problem as external wiring 110 of substrate 100.